Slurry reactors are well known for carrying out highly exothermic, three phase, catalytic reactions. Usually called "bubble columns" these reactors have a liquid phase in which solid catalyst particles are dispersed or held in suspension by a gas phase bubbling through the liquid phase, thereby creating a slurry. These reactors provide improved heat transfer characteristics for the exothermic reaction, and the bubbling gas provides essentially all of the energy necessary for maintaining the catalyst dispersed in the liquid phase.
Bubble column reactors typically have a multiplicity of tubes suspended within a shell-type housing, the tubes being filled with a heat transfer medium, e.g., steam, which absorbs the heat generated by the exothermic reaction occurring on the shell side of the tubes in the main body of the housing.
As previously stated, in slurry bubble columns, the catalyst particles are suspended by the gas entering the bubble columns through bottom sited distributors. Often, catalyst particles in these reactors are non-uniformly distributed in the axial direction of the reactor vessel within the range of gas velocities of interest to the practitioner. Under these conditions the reactor operation is limited by "hot spots" which are formed by stagnant zones of catalyst near the bottom of the column where the highest catalyst concentration is found or in stagnant zones. Non-uniform catalyst distribution also contributes to non-uniform catalyst aging and inefficient catalyst utilization insofar as the reaction progresses only when reactants are in contact with catalyst. In hydrocarbon synthesis processes such "hot spots" force the reactor to operate under less than maximum efficiency conditions.
It would be an advance if, in whatever configuration the reaction vessel may take, catalyst within the slurry reaction vessel could be more uniformly distributed and circulated so as to insure more even catalyst aging in the course of the reaction, more effective use of the catalyst by insuring a higher probability that the maximum amount of available catalyst is circulating in the reaction zone to promote the reaction by eliminating stagnant zones of standing catalyst.
In the downcomer, a separate hydrogen or any rejuvenating gas can be used to restore the catalyst activity by removing contaminants from the catalyst and liquid.